Apparatus and method for disabling the operation of high power devices

ABSTRACT

A drive circuit for delivering high-level power to a load, and method of stopping a high power load from operating, are disclosed. The drive circuit includes a high power circuit capable of being coupled to the load and delivering the high level power thereto, and a low power circuit that controls the high power circuit. The low power circuit includes a first circuit portion that provides at least one control signal that is at least indirectly communicated to the high power circuit and that controls the delivering of the high level power by the high power circuit, and a second circuit portions coupled to the first circuit portion. The second circuit portion is capable of disabling the first circuit portion so that the at least one control signal avoids taking on values that would result in the high power circuit delivering the high level power to the load.

CROSS-REFERENCE TO RELATED APPLICATIONS STATEMENT REGARDING FEDERALLYSPONSORED RESEARCH OR DEVELOPMENT FIELD OF THE INVENTION

The present invention relates to drive circuits that are used to controlthe delivery of high power levels to high power loads such as motorsand, more particularly, to the disabling of the power delivered by ofsuch drive circuits so that the loads are no longer driven.

BACKGROUND OF THE INVENTION

High power devices are commonly employed in a variety of environmentsincluding, for example, industrial facilities and constructionenvironments. High power devices generally include a variety ofdifferent devices including, for example, motors and heating devices.Although the operation of such devices under normal conditions does notpose undue risk, there are circumstances in which such devices must bereliably disabled so as not to pose risks to human beings or otherdevices.

For example, high power motors often rotate at high speeds and/orprovide significant torques that in certain situations could pose risksto human beings or other devices that come into contact with the motorsthemselves or with other devices coupled to those motors. In particular,when such motors or devices coupled to those motors are replaced, fixed,modified, tested or otherwise operated upon by human beings such asengineers or service technicians, it is desirable that the motors bereliably disabled such that the motors cease to rotate or deliversustained torque.

In view of the possible hazards associated with high power devicesgenerally, many modern industrial and other facilities employ variouselectronic and other technologies that reduce the risk of accidents andenhance overall system safety. Additionally, standards have beendeveloped with a goal of further reducing the risk of accidents. Forexample, with respect to industrial facilities, standards fromorganizations such as the NFPA, ISO, CEN, CENELEC, and the IEC have beendeveloped to establish requirements for safety. The technologies used toenhance system safety often are designed to comply with, or to assist inmaking a facility compliant with, standards from one or more of theseorganizations.

Some of the technologies employed to enhance system safety are designedto reliably disable high power devices. For example, technologies suchas high power contactors are often used to couple and decouple thedriven devices to and from their high power drive circuits. Suchcontactors often include multiple, redundant high power contacts thatare physically coupled to one another in such a way that, if one or moreof the contacts become locked/welded in position, a signal is providedindicating that a fault has occurred. The signal can be, for example,the turning on of an indicator light at an operator interface or simplythe failure of the high power device to start operating when commandedto do so.

Such high power contactors are often used because of their relativetechnical simplicity and reliability. Nevertheless, high powercontactors are disadvantageous insofar as they are relatively expensive,and physically large and bulky. Further, in certain circumstances, thedisconnecting and connecting procedures for implementing these highpower contactors can be complicated and/or time consuming. Consequently,the implementation of such high power contactors can negatively impactthe overall efficiency of an industrial or other system in which thehigh power devices are employed.

Because of these disadvantages, efforts have been made to find othermechanisms that could be used to disable high power devices. Onealternate method of disabling a high power motor that has beenattempted, for example, has involved disabling high power transistors ofa drive circuit that deliver the high levels of power to the motor.However, this method has thus far proven to be insufficiently reliable.

Therefore, it would be advantageous if a new mechanism could bedeveloped that allowed for reliable disabling of high power devices suchthat the high power devices could not inadvertently start operating in amanner that might present a hazard. In particular, it would beadvantageous if the new mechanism could avoid the disadvantagesassociated with using high power contactors in between the high powerdrive circuits and the driven devices, and at the same time was equallyor even more reliable than such high power contactors (or otherconventional technologies). Further, it would be advantageous if the newmechanism was relatively easy and inexpensive to implement.

SUMMARY OF THE INVENTION

The present inventors have recognized that, in some circumstances, highpower loads are satisfactorily disabled such that the loads stop movingor otherwise operating, regardless of whether high power levels of somesort continue to be provided to the loads. Indeed, in some of thesecircumstances, for example, the load is only capable of operating if itreceives carefully controlled power levels that vary in time in additionto being of high magnitude. With this in mind, the present inventorshave additionally recognized that in these circumstances it would bepossible to disable the operation of the loads simply by ceasing toprovide the control signals that govern the time-variation of the power.Further, the present inventors have recognized that, in situations wherethe drive circuits providing high power to their loads include both highpower drive sections and low power logic sections that provide controlsignals to the high power drive sections to govern the delivery ofpower, the disabling of the loads can be achieved simply by setting thecontrol signals of low power logic sections to low-level (or otherdisabling) values.

In particular, the present invention relates to a drive circuit fordelivering high-level power to a load. The drive circuit includes a highpower circuit capable of being coupled to the load and delivering thehigh level power thereto, and a low power circuit that controls the highpower circuit. The low power circuit includes a first circuit portionthat provides at least one control signal that is at least indirectlycommunicated to the high power circuit and that controls the deliveringof the high level power by the high power circuit, and a second circuitportions coupled to the first circuit portion. The second circuitportion is capable of disabling the first circuit portion so that the atleast one control signal avoids taking on values that would result inthe high power circuit delivering the high level power to the load.

The present invention additionally relates to a high power drive circuitfor delivering power to a motor. The high power drive circuit includesfirst means for delivering high power to the motor, second means forgenerating low power control signals for the first means, and thirdmeans for disabling the second means so that the low power controlsignals take on values that would tend to cause the first means to stopdelivering the high power to the motor.

The present invention also relates to a method of stopping a high powerload from operating, where the high power load receives power from adrive circuit having a high power drive section and a low power logicsection, and where the low power logic section provides a control signalto the high power drive section and the high power drive section duringnormal operation provides the power to the high power load in responseto the control signal. The method includes receiving a command to stopthe high power load from operating, and switching a status of at least afirst component of the low power logic section in response to thecommand. The switching of the status affects one of the first componentand a second component of the low power logic section so that thecontrol signal provided by the low power logic section takes on a valuethat would tend to cause the high power drive section to cease providingthe power to the high power load. The method further includes ceasing toprovide the power to the high power load in response to the controlsignal taking on the value.

The present invention additionally relates to a drive circuit fordelivering high-level power to a load. The drive circuit includes a highpower circuit capable of being coupled to the load and delivering thehigh level power thereto, and a low power circuit that controls the highpower circuit, where the low power circuit includes a first circuitportion that provides at least one control signal that is at leastindirectly communicated to the high power circuit and that controls thedelivering of the high level power by the high power circuit. Further,the first circuit portion is at least one of coupled to, and adapted tobe coupled to, a second circuit portion that is capable of providing tothe first circuit portion at least one additional signal causing thefirst circuit portion to become disabled so that the at least onecontrol signal avoids taking on values that would result in the highpower circuit delivering the high level power to the load.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a first exemplary embodiment of a drivecircuit coupled to a motor;

FIG. 2 is a schematic diagram of a second exemplary embodiment of adrive circuit coupled to a motor; and

FIG. 3 is a schematic diagram of a third exemplary embodiment of a drivecircuit coupled to a motor.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an exemplary drive circuit 10 for providing highlevels of power to a motor 20 is shown. The drive circuit 10 includes ahigh power drive section 30 and a low power logic section 40. The highpower drive section 30 also can be termed a power structure, while thelow power logic section 40 can be termed a control structure.

As shown, first, second and third phases of power 32, 34 and 36,respectively, are delivered to the motor 20 from six power transistordevices 41-46. In the present embodiment, each of the power transistordevices 41-46 is an insulated gate bipolar transistor (IGBT) although,in alternate embodiments, other types of power transistor devices (orother, non-transistor power delivery devices) can be used. Each of thefirst, second and third phases 32, 34 and 36 receives voltage from arespective pair of the power transistor devices 41-42, 43-44, and 45-46,respectively. Current flows toward or away from the motor 20 in eachphase 32, 34, 36 depending upon which of the pair of corresponding powertransistor devices is switched on. If neither of the power transistordevices of a given pair is on, no current flows toward or away from themotor in the corresponding phase. First, second and third coils 50, 52and 54, respectively, are coupled in series between the motor 20 andeach of the respective pairs of power transistor devices 41-42, 43-44and 45-46. By virtue of the first, second and third coils 50, 52 and 54,the respective currents in each of the respective first, second andthird phases 32, 34 and 36 can be sensed using conventional currentsensing componentry (not shown).

Each of the power transistor devices 41-46 is electrically isolated fromthe remainder of the high power drive section 30 and the low power logicsection 40. However, the switching on and off of the power transistordevices 41-46 is nevertheless governed by signals coming from theremainder of the high power drive section 30. As shown, the powertransistor devices 41-46 are light sensitive devices that respond tolight signals given off by six optocoupler photodiodes 61-66,respectively. The six photodiodes 61-66 are turned on and off based uponsix control signals provided from the low power logic section 40, whichare respectively provided by six control line outputs 71-76 of the lowpower logic section 40. More specifically, the six photodiodes 61-66 arethemselves grouped into three pairs of photodiodes 61-62, 63-64 and65-66. The photodiodes of each of the pairs are coupled in parallel withone another in opposite orientations, and the nodes linking the twophotodiodes of each pair are then coupled to respective ones of thecontrol line outputs 71-76 by way of respective resistors 70. Althoughshown as part of the high power drive section 30, the resistors 70 andphotodiodes 61-66 are low power devices; they are considered to be partof the high power drive section insofar as they are in directcommunication with the high power transistor devices 41-46, and insofaras in practice the photodiodes are typically (though not necessarily)mounted on the same circuit board as the power transistor devices ratherthan on a separate circuit board supporting the low power logic section.Depending upon the embodiment, the respective photodiodes 61-66 aredevices that are physically separate from the respective powertransistor devices 41-46 or, alternately, the respective photodiodes arepackaged along with their corresponding power transistor devices 41-46in an integrated manner.

Further as shown in FIG. 1, the low power logic section 40 includes amicroprocessor 80 that is coupled to a hex inverter with open collectoroutput 90, which in turn is connected to an octal tri-state buffer/linedriver 100. The driver 100 outputs the control signals on the controlline outputs 71-76 in response to six inverter signals provided by thehex inverter 90 on six inverter signal lines 91-96. The six invertersignals on lines 91-96 are provided by the inverter 90 in response tosix microprocessor signals output by the microprocessor 80 on sixmicroprocessor signal lines 81-86. Each of the microprocessor signallines 81-86 is coupled not only to a respective input terminal on thehex inverter 90 but also is coupled to a power supply 99 by way of arespective pull-up resistor 98. The power supply 99 is also coupled tothe microprocessor 80 to provide power thereto. In the presentembodiment, the power supply for the low power logic section 40 is apositive 5 volt DC power supply, and each of the pull-up resistors 98 isa 10 kΩ resistor. The hex inverter 90 essentially consists of sixinverter components 97, each of which inverts a respective one of themicroprocessor signals provided by way of lines 81-86 to produce theinverter signals provided on lines 91-96, respectively.

During normal operation, the driver 100 merely acts as a buffer betweenthe inverter signal lines 91-96 and the control line outputs 71-76. Thatis, the signal level of each respective control line output 71-76 is thesame as the signal level of the corresponding inverter signal line91-96. The buffering performed by the driver 100 is provided by way ofsix buffer components 102 within the line driver 100, each of which iscoupled respectively between a respective one of the control lineoutputs 71-76 and its corresponding inverter signal line 91-96. Further,because during normal operation the inverter 90 merely inverts thesignals output by the microprocessor 80 along lines 81-86, the signalsoutput by the driver 100 on the control line outputs 71-76 during normaloperation have values that are opposite/inverted relative to the valuesof the signals on the lines 81-86.

The driver 100 does not, however, output signals on lines 71-76 that arethe same as those on lines 91-96 and inverted relative to those on lines81-86 in all circumstances. Rather, the driver 100 only outputs thecorrect signals on lines 71-76 in response to the inverter signals onlines 91-96 if three conditions are met. First, power must be providedto the driver 100. Second, each of the lines 91-96 is coupled to arespective pull-up resistor 104, and each of these pull-up resistorsmust in turn be provided with power. In the embodiment shown, the powersupply to which the resistors 104 are coupled can again be a positive 5volt DC power supply, and each of the pull-up resistors 104 can have avalue of 4.7 kΩ. Third, power must be provided to an enable input 106 ofthe driver 100, which in turn results in the enabling of each of thebuffer components 102. If any of these conditions are not met, thedriver 100 ceases to consistently provide signals on lines 71-76 thatare the same as the signals on lines 91-96 and inverted relative to thesignals on lines 81-86, and instead the signals output by the drivereach take on a zero value or effectively-zero value in which no currentis conducted to any of the photodiodes 61-66.

The failure to meet any one of these conditions results in the controlline outputs 71-76 being nonconductive for the following reasons. If thepower supply is decoupled from the pull-up resistors 104, then currentswill not flow through those resistors 104 when the inverter signal lines91-96 take on a zero value. Further, because the inverter 90 is an opencollector output device, the absence of power being supplied to thepull-up resistors 104 causes the six inverter components 97 of theinverter to enter high impedance, indeterminate states. While theinverter components 97 are in these indeterminate states, they areunable to take on high voltage values, and consequently, the lines 91-96and input terminals of the buffer components 102 of the driver 100remain at zero volts. Likewise, if the power supply 99 is entirelydecoupled from the driver 100 itself, the buffer components 102 areunable to output nonzero currents on the control output lines 71-76.Further, if a zero voltage level is applied to the enable input 106 ofthe driver 100, then each of the buffer components 102 likewise isunable to provide a nonzero current on any of the control output lines71-76.

In accordance with one embodiment of the present invention, thesefeatures of the low power logic section 40 are employed to provide tworedundant mechanisms for shutting down the low power logic section suchthat none of the power transistor devices 41-46 is commanded by any ofthe photodiodes 61-66 to deliver high power to the motor 20.Specifically, a first mechanism for shutting down the low power logicsection 40 involves a safety relay circuit 110 that governs whether thepower supply 99 is coupled to each of the pull-up resistors 104 as wellas to the driver 100 itself. As shown, the safety relay circuit 110includes a safety on input 112 that includes a coil 114. So long as apredetermined voltage level is applied across the coil 114 (for example,24 volts), a normally-open contact 116 within the safety relay circuit110 is closed and a second, normally-closed contact 118 within thesafety relay circuit is opened. The closing of the normally-open contact116 links first and second ports 120, 122 of the safety relay circuit110 so that the power supply 99, which is coupled to the first port 120,is in turn coupled to the pull-up resistors 104 and the driver 100itself, each of which are coupled to the second port 122. However, ifthe necessary voltage is no longer applied across the coil 114, then thepower supply 99 is decoupled from both the pull-up resistors 104 and thedriver 100 itself, thus causing the control output lines 71-76 to shutoff and provide no voltage. Therefore, by applying or not applying avoltage across the coil 114 of the safety relay circuit 110, an operatorcan thereby determine whether the signals on control line outputs 71-76reflect the microprocessor signals on lines 81-86 to provide normalcontrol of the motor 20, or take on null values such that the powertransistor devices 41-46 do not provide voltage to the motor 20.

The present embodiment is further designed to allow for the detection offaults in the safety relay circuit 110. Specifically, a safety onmonitor can also be coupled to third and fourth ports 124, 126 of thesafety relay circuit 110, between which is coupled the normally-closedcontact 118. The safety relay circuit 110 is configured such that thenormally-open contact 116 and normally-closed contact 118 are physicallycoupled so that only one or the other of the contacts can be closed atany given time. Consequently, if the voltage applied across the coil 114is turned off and the normally-open contact 116 remains closed, then thenormally-closed contact 118 remains open and thus the safety on monitorcan determine that a fault has occurred due to the open-circuiting ofthe third and fourth ports 124, 126 and the information that the voltagehas been disconnected from the coil 114. Conversely, if thenormally-closed contact 118 becomes welded, then the normally-opencontact 116 cannot close despite the providing of voltage across thecoil 114, and consequently the driver 100 cannot provide nonzero signalson the control line outputs 71-76.

In addition to the control capability provided by way of the safetyrelay circuit 110 in terms of controlling whether power is provided tothe pull-up resistors 104 and to the driver 100, the embodiment of FIG.1 also includes additional logic circuitry 130 that determines whetherthe enable input 106 of the driver 100 is asserted. As shown, theadditional logic circuitry 130 includes a hardware switch 132 that iscoupled between ground 134 (which is also coupled to appropriategrounding terminals on the microprocessor 80, the inverter 90 and thedriver 100) and a low-true input 136 of a NOR gate 138. A secondlow-true input 140 of the NOR gate 138 is coupled to the microprocessor80 by way of a control line 142, such that the microprocessor can alsoprovide an input to the NOR gate. The output of the NOR gate 138 iscoupled to a buffer component 144, which in turn is coupled to theenable input 106 and also to a further pull-up resistor 146. The furtherpull-up resistor 146 is coupled to the power supply 99 by way of thesame line as the other pull-up resistors 104, such that power is onlysupplied when the normally-open contact 116 of the safety relay circuit110 is closed. The buffer 144 acts as an open collector output such thata positive, non-zero output can only be applied to the enable input 106of the driver 100 if power is supplied to the pull-up resistor 146, thatis, only if the normally-open contact 116 of the safety relay circuit110 is closed.

Given this design, the enable input 106 only receives a positive,non-zero value such that the driver 100 is capable of outputtingnon-zero output signals on the control line outputs 71-76 if thenormally-open contact 116 of the safety relay circuit 110 is closed andat least one of the hardware switch 132 is closed or the microprocessor80 provides a zero-level control signal via the control line 142 to theinverter 140. Thus, even if the safety relay circuit 110 is actuatedsuch that power is provided to each of the driver 100 and the pull-upresistors 104, 146, it is possible for either of the microprocessor 80or an operator, by way of opening the switch 132, to disable the driver100 such that each of the control line outputs 71-76 takes on a zero oreffectively-zero level.

When implemented as shown in FIG. 1, the drive circuit 10 providesmultiple, redundant avenues by which an operator or other control entitycan cause the drive circuit to provide zero-level control signals viathe control line outputs 71-76 to the photodiodes 61-66 such that themotor 20 ceases to receive power from the power transistor devices41-46. While it is possible that a human operator may trigger one orboth of the hardware switch 132 or the safety on input 112 of the safetyrelay circuit 110, the present embodiment also envisions the coupling ofthese inputs to other components such as an additional safety relaycircuit that would be capable of providing a command to each of theseinputs (such a safety relay circuit could, for example, be present in afactory environment). That is, the present embodiment is intended to becapable of being implemented in conjunction with a variety of otherdevices in a manner allowing those other devices to control whether thedrive circuit 10 is disabled.

The circuitry of the drive circuit 10 also is sufficiently redundantthat it satisfies requirements of Category 3 of the EN 954-1 standard,which requires that no single fault in any part of the drive circuit 10would lead to a loss of the ability to cease providing control signalssuch that the motor 20 might develop sustained torque. As discussedabove, a failure of one of the contacts of the safety relay circuit 110can be detected by way of the safety on monitor. In the case of theactuation of the switch 132 or a microprocessor command provided by wayof the control line 142, a failure of the signals on control lineoutputs 71-76 to become null in response to such activation/command canbe sensed by way of the coils 50, 52 and 54. That is, if the switch 132is open, or the microprocessor 80 is providing a zero-level signal onthe control line 142, then none of the coils 50, 52, 54 shouldexperience any current and, if current is sensed, a warning signal isgenerated. In certain embodiments, the sensed current informationobtained by way of the coils 50, 52 and 54 is provided to and used bythe microprocessor 80.

The fact that the drive circuit 10 satisfies Category 3 of the EN 954-1standard is not meant to indicate that the drive circuit 10 guaranteesthat electrical voltage is not provided to the motor 20. Indeed, despitethe nullification of the control line outputs 71-76, it is stillconceivable that one or more of the power transistor devices 41-46 wouldapply voltage to the motor 20. Rather, because the motor 20 can onlydevelop sustained rotation and torque if the power transistor devices41-46 apply voltage at specific times in a pulse width modulated (PWM)manner determined by the microprocessor 80, inadvertent conduction ofcurrents by any of the power transistor devices 41-46 would only, atmost, cause the motor to experience a one-time movement of a limitednumber of degrees, such as 180 degrees for a two-pole motor or 90degrees for a four-pole motor. If the motor 20 is running when eitherthe safety on input 112 is triggered or the enable input 106 receives alow level signal due to the triggering of the switch 132 or a signalfrom the microprocessor 80, the motor 20 will coast to a standstill. Thesafety relay circuit input to the driver 100 prevents power from beingprovided to the control line outputs 71-76, while the actuation of theenable input 106 of the driver 100, as actuated by the switch 132 or themicroprocessor 80 by way of the control line 142, acts as a logicinhibit of the control line outputs.

Turning to FIG. 2, an alternate embodiment of a drive circuit 210 thatsomewhat differs from the drive circuit 10 of FIG. 1 is shown coupled tothe motor 20. The drive circuit 210 does include the same high powerdrive section 30 as the drive circuit 10, and a low power logic section240 of the drive circuit includes the same microprocessor 80, inverter90, pull-up resistors 98, 104 and 146, and additional logic circuitry130 as the low power logic section 40. As in the case of drive circuit10, the additional logic circuitry 130 provides signals to an enableinput 106 of an octal tri-state buffer/line driver 200 of the logiccircuit 240. However, the logic circuit 240 differs from the logiccircuit 40 in that the driver 200 of the logic circuit 240 is notcoupled to the power supply 99 by way of any safety relay. Further, asafety relay circuit 310 that is employed in the low power logic section240 is essentially an inverted version of the safety relay circuit 110.Namely, the safety relay circuit 310 includes first and second ports 320and 322 that are respectively coupled to the ground 134 and to thepull-up resistors 104 and 146, with a normally-closed contact 316coupled between those ports. Also, third and fourth ports 324 and 326 ofthe safety relay circuit 310 have a normally-open contact 318 coupledbetween them. Further, the power supply 99 is coupled to the pull-upresistors 104 and 146 and to the second port 322 by a low-levelresistance (in this example, a 330 ohm resistor).

Consequently, when a safety on input is provided to the safety relaycircuit 310 such that a coil 312 within the safety relay circuit isactuated, the normally-closed contact 316 is opened such that the powersupply 99 is effectively connected to the pull-up resistors 104, 146,thereby allowing the driver 200 to receive non-zero signals from theinverter 90. However, when the safety on input is not provided to thesafety relay circuit 310, the pull-up resistors 104 and 146 are coupledto ground, thereby preventing the driver 200 from outputting non-zerosignals on the control line outputs 71-76. As in the case of the safetyrelay circuit 110, the normally-closed contact 316 and normally-opencontact 318 of the safety relay circuit 310 are physically coupled suchthat only one of the contacts can be closed at any given time, such thata welding of either of the normally-closed and normally-opened contactscan be detected. In comparison with the drive circuit 10 of FIG. 1, thedrive circuit 210 of FIG. 2 is somewhat simpler to implement and forthat reason is somewhat preferred for that reason, albeit the embodimentof FIG. 1 satisfies certain standards that may not be satisfied by thecircuit of FIG. 2.

Referring to FIG. 3, yet a third embodiment of the present inventionshows a drive circuit 410 having components identical to the drivecircuit 110 except insofar as the safety relay circuit 110 has beenreplaced with a circuit 400 that includes a DC-to-DC conversion circuit420. In this embodiment, it is envisioned that another device (notshown) such as another safety relay circuit provided by a third partywould be coupled to input terminal 412 of the circuit 400. The circuitwould then convert power signals provided by that other device into anoutput signal 415 that would govern the voltage applied to the pull-upresistors 104, 146 and the power supplied to the driver 100. By using aDC-to-DC conversion circuit such as that shown, the input signals at theinput terminal 412 would be isolated from the output signal 415, and theinput signals could differ in their voltage range from that required bythe driver 100 in an arbitrary manner (in the embodiment shown, forexample, the input signals 412 can range from 0 to 12 Volts signals,while the output signal 415 can range from 0 to 5 Volts). Although theembodiment of FIG. 3 shows a DC-to-DC conversion circuit that provideselectrical isolation, in alternate embodiments, opto-isolators or otherdevices could be employed to provide isolation. A DC-to-DC conversiondevice is advantageous insofar as it provides a reliable shut-downmechanism since it cannot operate without power being applied.

Although three embodiments of the present invention are shown in FIGS.1-3, the present invention is not intended to be limited to theseparticular electrical circuits. Rather, the present invention isintended to encompass a variety of electrical and other control circuitsin which the delivery of high power levels to a high power device isgoverned in part by low power circuitry, and in which there are one ormore control mechanisms for disabling the low power circuitry toeffectively stop the operation of the high power device without takingany action to disable or disconnect the high power drive circuit devicesthat are directly coupled to that high power load. Indeed, the presentinvention is intended to encompass any such dual-stage drive circuits inwhich disablement occurs via the low power stage, regardless of the typeof high power load that those drive circuits are powering.

Also, the present invention is intended to encompass control/drivecircuits that are formed from multiple distinct modules. For example,with respect to the embodiment of FIG. 2, all of the components of thedrive circuit 210 need not be included on a single circuit board.Rather, in some embodiments, all of the low power logic circuit 240 ofthe drive circuit 210 of FIG. 2 would be included within a primarymodule except for the safety relay circuit 310, which could beimplemented on an auxiliary module. In such an embodiment, the drivecircuit 210 could be operated to control the high power drive circuit 30and the motor 20 as normal without the auxiliary module. However, if theauxiliary module were coupled to the primary module (e.g., by way ofappropriate connectors/adaptors), then it would be further possible todisable the drive circuit as discussed above by providing the safety oninput and thereby coupling the pull-up resistors 104, 146 to the ground.A similar design could be employed in relation to the embodiments ofFIGS. 1 and 3, particularly if a jumper was used to couple the pull-upresistors 104,146 and power input of the driver 100 to a power supply inthe absence of the safety relay circuit 110 or the circuit 400. Anauxiliary module including a safety relay circuit or other circuit suchas circuits 110,310 and 400 could be implemented in a variety ofmanners, such as on a plug-in-module or as part of an external cable.Thus, the present invention is intended to encompass embodiments inwhich a main control device can be coupled to one or more other devices,which depending upon the embodiment might be required or optional (oreven after-market) devices.

Although the terms “safety”, “reliable”, “safety system”, “safetycontroller”, and other related terms may be used herein, the usage ofsuch terms is not a representation that the present invention will makean industrial or other process safe or absolutely reliable, or thatother systems will produce unsafe operation. Safety in an industrial orother process depends on a wide variety of factors outside of the scopeof the present invention including, for example: design of the safetysystem; installation and maintenance of the components of the safetysystem; the cooperation and training of individuals using the safetysystem; and consideration of the failure modes of the other componentsbeing utilized. Although the present invention is intended to be highlyreliable, all physical systems are susceptible to failure and provisionmust be made for such failure.

The above description has been that of a preferred embodiment of thepresent invention. It will occur to those that practice the art thatmany modifications may be made without departing from the spirit andscope of the invention. In order to apprise the public of the variousembodiments that may fall within the scope of the invention, thefollowing claims are made.

1. A drive circuit for delivering high-level power to a load, the drivecircuit comprising: a high power circuit capable of being coupled to theload and delivering the high level power thereto; and a low powercircuit that controls the high power circuit, wherein the low powercircuit includes a first circuit portion that provides at least onecontrol signal that is at least indirectly communicated to the highpower circuit and that controls the delivering of the high level powerby the high power circuit; and a second circuit portion coupled to thefirst circuit portion, wherein the second circuit portion is capable ofdisabling the first circuit portion so that the at least one controlsignal avoids taking on values that would result in the high powercircuit delivering the high level power to the load.
 2. The drivecircuit of claim 1, further comprising a third circuit portion that alsois coupled to the first circuit portion, wherein the third circuitportion also is capable of disabling the first circuit portion so thatthe at least one control signal avoids taking on values that wouldresult in the high power circuit delivering the high level power to theload.
 3. The drive circuit of claim 1, wherein the second circuitportion includes a safety relay circuit that is coupled to a powerterminal of the first circuit portion, and wherein the safety relaycircuit decouples the power terminal of the first circuit from a powersupply in order to disable the first circuit portion.
 4. The drivecircuit of claim 1, wherein the second circuit portion includes a safetyrelay circuit that is coupled to a pull-up resistor of the first circuitportion, and wherein the safety relay circuit disables the first circuitportion by at least one of coupling the pull-up resistor to ground anddecoupling the pull-up resistor from a power supply.
 5. The drivecircuit of claim 4, wherein the safety relay circuit additionally iscoupled to a power terminal of the first circuit portion, and whereinthe safety relay circuit couples the power terminal of the first circuitportion to ground in order to further disable the first circuit portion.6. The drive circuit of claim 4, wherein the safety relay circuitincludes a coil, a normally-open contact, and a normally-closed contact,wherein the contacts are physically coupled so that only one of thecontacts can be closed at any given time, and wherein the safety relaycircuit disables the first circuit portion when power is provided to thecoil.
 7. The drive circuit of claim 1, wherein the second circuitincludes a component that is coupled to an override port of the firstcircuit, and wherein the second circuit disables the first circuit byproviding a first signal to the override port of the first circuit. 8.The drive circuit of claim 7, wherein the second circuit includes ahardware switch that is capable of being switched between first andsecond states, and wherein when the switch is switched in the firststate, the second circuit provides the first signal to the override portof the first circuit.
 9. The drive circuit of claim 8, wherein thesecond circuit further includes a NOR gate having first and second inputterminals, wherein the NOR gate receives a second signal from thehardware switch and a third signal from the first circuit at the firstand second input terminals, and wherein the NOR gate outputs a fourthsignal that is one of equal to or functionally related to the firstsignal.
 10. The drive circuit of claim 8, wherein the high power circuitincludes at least one coil that outputs a signal indicative of a currentdelivered by the high power circuit to the load, and wherein adetermination is made regarding whether the signal indicative of thecurrent is proper when the switch is switched in the first state. 11.The drive circuit of claim 1, wherein the first circuit includes amicroprocessor, an inverter circuit, and a buffer circuit.
 12. The drivecircuit of claim 11 wherein, when the first circuit is not disabled, themicroprocessor outputs a plurality of preliminary signals to theinverter circuit, the inverter circuit converts the plurality ofpreliminary signals into a plurality of modified signals, and the buffercircuit provides the at least one control signal in response to theplurality of modified signals, and each of the preliminary signals, themodified signals, and the at least one control signal is a pulse widthmodulated (PWM) signal.
 13. The drive circuit of claim 11, wherein theinverter circuit has open collector output terminals that are coupled tothe buffer circuit, wherein the second circuit portion includes a safetyrelay circuit that is coupled to a pull-up resistor that is coupledbetween the safety relay circuit and both one of the open collectoroutput terminals and a corresponding input terminal of the buffercircuit, and wherein the safety relay circuit at least one of decouplesthe pull-up resistor from a power supply and couples the pull-upresistor to a ground in order to disable the first circuit portion. 14.The drive circuit of claim 13, wherein the safety relay circuit also iscoupled to an additional pull-up resistor that is coupled to a thirdcircuit portion that is coupled to an enable input of the buffercircuit, and wherein the safety relay circuit at least one of decouplesthe additional pull-up resistor from the power supply and couples theadditional pull-up resistor to the ground in order to further disablethe first circuit portion by disabling the buffer circuit.
 15. The drivecircuit of claim 1, wherein the high power circuit includes a pluralityof high power transistor devices that are light-actuated and a pluralityof photodiodes receive the at least one control signal from the lowerpower circuit, and wherein the high power transistor devices areelectrically isolated from the photodiodes.
 16. The drive circuit ofclaim 1, wherein the second circuit portion includes an isolation devicethat is capable of communicating a signal provided from an additionaldevice to the first circuit portion.
 17. The drive circuit of claim 16,wherein the isolation device includes one of a DC-to-DC converter and anoptical isolator.
 18. A high power drive circuit for delivering power toa motor, the high power drive circuit comprising: first means fordelivering high power to the motor; second means for generating lowpower control signals for the first means; and third means for disablingthe second means so that the low power control signals take on valuesthat would tend to cause the first means to stop delivering the highpower to the motor.
 19. The high power drive circuit of claim 18,wherein the third means includes at least first and second inputs thatcan be independently switched to cause the third means to disable thesecond means.
 20. A method of stopping a high power load from operating,wherein the high power load receives power from a drive circuit having ahigh power drive section and a low power logic section, and wherein thelow power logic section provides a control signal to the high powerdrive section and the high power drive section during normal operationprovides the power to the high power load in response to the controlsignal, the method comprising: receiving a command to stop the highpower load from operating; and switching a status of at least a firstcomponent of the low power logic section in response to the command,wherein the switching of the status affects one of the first componentand a second component of the low power logic section so that thecontrol signal provided by the low power logic section takes on a valuethat would tend to cause the high power drive section to cease providingthe power to the high power load; and ceasing to provide the power tothe high power load in response to the control signal taking on thevalue.
 21. The method of claim 20, wherein the switching of the statusincludes at least one of the following: decoupling a power supply from apower supply terminal of a buffer circuit of the low power logicsection; decoupling a power supply from a pull-up resistor of the lowpower logic section, wherein the pull-up resistor is also coupled toboth an output of an inverter circuit having an open collector outputand an input of the buffer circuit; coupling the pull-up resistor of thelow power logic section to a ground; and providing an intermediatesignal to an enable/disable port of the buffer circuit such that thebuffer circuit becomes disabled.
 22. The method of claim 20, wherein thecommand is provided by way of at least one of an actuation of acomponent in a safety relay circuit, an actuation of a hardware switch,and a sending of a signal from a control component within the low powerlogic section.
 23. A drive circuit for delivering high-level power to aload, the drive circuit comprising: a high power circuit capable ofbeing coupled to the load and delivering the high level power thereto;and a low power circuit that controls the high power circuit, whereinthe low power circuit includes a first circuit portion that provides atleast one control signal that is at least indirectly communicated to thehigh power circuit and that controls the delivering of the high levelpower by the high power circuit; wherein the first circuit portion is atleast one of coupled to, and adapted to be coupled to, a second circuitportion that is capable of providing to the first circuit portion atleast one additional signal causing the first circuit portion to becomedisabled so that the at least one control signal avoids taking on valuesthat would result in the high power circuit delivering the high levelpower to the load.